A comprehensive theoretical study of excluded volume effects upon biochemical equilibria and kinetics has been carried out. The self-association of myoglobin in concentrated solution and in the presence of high concentrations of globular proteins has been studied by measurement of sedimentation equilibrium and fluorescence polarization. The effect of thermodynamic nonideality upon the partition coefficient measured in exclusion chromatography has been theoretically studied. A quantitative model for hormone action has been formulated and applied to the analysis of experimental data.